MAGNETISM AND ITS USES Electricity and Magnetism Chapter 8, Section 2 Notes MAGNETISM AND ITS USES Electricity and Magnetism
Big Idea: An electric current in a wire is surrounded by a magnetic field. Moving charges and magnetic fields 1. Moving charges, like those in an electric current, produce magnetic fields. a. The magnetic field around a current- carrying wire forms a circular pattern about the wire. See page 231.
The direction of the field depends on the direction of the current. The strength of magnetic field depends on the amount of current flowing in the wire.
Electromagnet – a temporary magnet made by placing a piece of iron inside a current- carrying coil of wire. See page 232. 1. Magnetic field is present only when current is flowing in the wire coil. 2. Increase strength of the magnetic field by adding more turns to the wire coil or increasing the current passing through the wire.
Magnetic properties of electromagnets can be controlled by changing the electric current flowing through the wire coil. Converts electrical energy into mechanical energy to do work. Examples include stereo speakers and electric motors. See pages 233- 234.
Galvanometer – a device that uses an electromagnet to measure electric current. See page 235. Example: Car fuel tank. Electric Motor – a device that changes electrical energy into mechanical energy. See pages 235 – 236.
Contains an electromagnet that is free to rotate between the poles of a permanent, fixed magnet. The coil in the electromagnet is connected to a source of electric current. When a current flows through the electromagnet, a magnetic field is produced in the coil.
Changing the direction of the current causes the coil in an electric motor to keep rotating. Rotation speed of electric motors can by controlled. a. Vary the amount of current flowing through the coil.
b. When more current flows through the coil, the electromagnet’s magnetic field becomes stronger, the magnetic force between the coil and the permanent magnet increase, and the coil turns faster.